Unregister pthread_atfork handlers on dlclose()

Bug: http://b/20339788
Change-Id: I874c87faa377645fa9e0752f4fc166d81fd9ef7e
diff --git a/libc/arch-common/bionic/crtbegin.c b/libc/arch-common/bionic/crtbegin.c
index fa9f3f3..c46405c 100644
--- a/libc/arch-common/bionic/crtbegin.c
+++ b/libc/arch-common/bionic/crtbegin.c
@@ -59,6 +59,7 @@
 
 #include "__dso_handle.h"
 #include "atexit.h"
+#include "pthread_atfork.h"
 #ifdef __i386__
 # include "../../arch-x86/bionic/__stack_chk_fail_local.h"
 #endif
diff --git a/libc/arch-common/bionic/crtbegin_so.c b/libc/arch-common/bionic/crtbegin_so.c
index 641e45a..3754363 100644
--- a/libc/arch-common/bionic/crtbegin_so.c
+++ b/libc/arch-common/bionic/crtbegin_so.c
@@ -56,6 +56,7 @@
 # include "__dso_handle_so.h"
 # include "atexit.h"
 #endif
+#include "pthread_atfork.h"
 #ifdef __i386__
 # include "../../arch-x86/bionic/__stack_chk_fail_local.h"
 #endif
diff --git a/libc/arch-common/bionic/pthread_atfork.h b/libc/arch-common/bionic/pthread_atfork.h
new file mode 100644
index 0000000..0c48a12
--- /dev/null
+++ b/libc/arch-common/bionic/pthread_atfork.h
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+extern void* __dso_handle;
+
+extern int __register_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void), void* dso);
+
+#ifndef _LIBC
+// Libc used to export this in previous versions, therefore it needs
+// to remain global for binary compatibility.
+__attribute__ ((visibility ("hidden")))
+#endif
+int pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void)) {
+  return __register_atfork(prepare, parent, child, &__dso_handle);
+}
+